Staining characteristics and antiviral activity of sulforhodamine B and lissamine green B.

PURPOSE: Fluorescein and rose bengal are dyes used routinely in the examination of the ocular surface. As part of an ongoing search for a superior ophthalmic dye with optimal specificity and sensitivity and a lack of interference with subsequent viral cultures, and as part of studies that use chemical dyes to understand better the pathophysiology of ocular surface disorders, the staining characteristics and antiviral activity of sulforhodamine B and lissamine green B were investigated.
METHODS: Staining of rabbit corneal epithelial cell cultures by sulforhodamine B and lissamine green B was compared to that of fluorescein and rose bengal. Diffusion of each dye through a collagen gel was measured. Uptake of lissamine green B by herpes simplex virus type 1 (HSV-1)-infected Vero cell cultures was compared at several times postinfection. The effect of sulforhodamine B and lissamine green B on HSV-1 plaque formation in Vero cells was determined. The cellular toxicity of sulforhodamine B and lissamine green B in vitro was examined by a quantitative 14C-amino acid uptake assay and by a qualitative cell viability assay. Finally, the effect of sulforhodamine B and lissamine green B on viral replication was compared in vivo with that of rose bengal in a rabbit model of herpetic epithelial keratitis.
RESULTS: Rose bengal vividly stained cell monolayers of explant cultures of rabbit corneal epithelium. By light microscopy, sulforhodamine B and lissamine green B, like fluorescein, did not stain the epithelial cells, but did stain the corneal explant stroma. Pretreatment of epithelial cells with 0.25% trypsin for 5 minutes failed to induce dye uptake; however, pretreatment with 0.5% Triton X-100 for 5 minutes resulted in nuclear staining by lissamine green B, but not sulforhodamine B. When added to a collagen gel, the relative diffusion rate was fluorescein > lissamine green B > sulforhodamine B > rose bengal. By spectrophotometric analysis, HSV-1-infected and uninfected Vero cells bound equivalent amounts of lissamine green B until late in infection, when infected cells took up more dye (P < 0.001). A direct neutralization assay showed that 0.06% lissamine green B or 0.5% sulforhodamine B reduced HSV-1 plaque formation in Vero cells by greater than 50%, when present at the time of viral adsorption. By a quantitative 14C-amino acid uptake assay, lissamine green B was toxic to Vero cells in a dose-dependent manner, whereas sulforhodamine B was relatively nontoxic at the concentrations tested. By a cell viability assay, however, neither dye showed significant cellular toxicity. In a rabbit model of herpetic epithelial keratitis, rose bengal significantly reduced viral replication and recovery, whereas sulforhodamine B and lissamine green B had no effect.
CONCLUSIONS: Neither sulforhodamine B nor lissamine green B stain healthy, normal cells. Lissamine green B stains membrane-damaged epithelial cells, but sulforhodamine B does not. Both sulforhodamine B and lissamine green B stain corneal stroma. Lissamine green B inhibits HSV-1 plaque formation at low concentrations of dye in vitro, which correlates with suppression of cellular metabolism as demonstrated by a 14C-amino acid uptake assay, but does not affect cell viability. Neither sulforhodamine B nor lissamine green B inhibit viral replication or recovery in vivo.